1. What ingredients should you look for in teeth whitening products and why? Be
specific, include studies, etc. -- Carbamide peroxide is the active ingredient. It is essentially hydrogen peroxide but in a longer-lasting form that has time to penetrate the lattice crystal structure in our teeth before breaking down. A higher % of carbamide peroxide means the mixture is more powerful, but can increase tooth sensitivity as well. PAP seems to also be effective but hasn't been as extensively studied as peroxides, meaning its long-term safety and efficacy is more uncertain.
2. What ingredients (common allergens, toxic, etc.) should you avoid in teeth whitening products and why? Be specific, include studies, etc. -- there are few allergenic compounds or toxins in whitening products made in the USA or by US companies due to FDA regulations to sell these products here. However, be very careful buying bleaching from companies located overseas outside of Europe and other first-world countries (for example, I'd be very careful buying anything out of China, etc).
3. Which is better: LED whitening kits, whitening kits without lights
(trays/gel), or whitening strips? What are the pros/cons of all
three? It has all has to do with how long the bleaching solution sits on your teeth and what % carbamide peroxide it contains. You can occasionally find a few products with simple hydrogen peroxide but that compound is not active for as long. The lights appear to have minor effects at lower concentrations of peroxide (https://www.sciencedirect.com/science/article/abs/pii/S1572100018304241) but much of their effect is drying out the teeth, which creates a temporary lighter appearance. Whitening strips can be fine but usually they struggle to hold the bleaching solution against the teeth for as long as fitted bleaching trays without washing out. PAP seems to also be somewhat effective and can be used in a similar way but again has less research into its long-term safety and efficacy.
4. What other things should you look for in whitening
products? Application time, best whitening method, % of active
ingredients, ADA approval, etc. - the ADA does not approve bleaching solutions because it is not shown to decrease dental disease, which is what the ADA seal is for. Application time is inversely proportional to the strength of the product, meaning 40% carbamide peroxide solutions are applied for much shorter times than 10% carbamide peroxide solutions. The best bang for your buck is a simple gel of carbamide peroxide solution in a fitted bleaching tray. Gels are commonly distributed in syringes, but any distribution method that allows for targeted application of the gel into a well-fitted tray is ideal. Start with a lower % of carbamide peroxide then work to higher %s as you feel out what your teeth can tolerate when it comes to sensitivity.
5. How can someone choose the right whitening product for their needs? Who shouldn't whiten their teeth? When should you seek professional whitening over
at-home options? - choose a reputable company used by dentists and made in a first world country. Don't whiten your teeth if you have extreme tooth sensitivity or you need cavities filled or root canal performed because it can inflame the nerves in the teeth. All teeth bleaching can be done at home unless there is a specific timeline (i.e. wedding) or a tooth has gotten dark on the inside, often due to a root canal or dead tooth (in that case, internal bleaching at your dentist or root canal specialist [endodontist] is the solution).
6. Do LED lights actually make a different in teeth whitening? What are the pros/cons/alternatives? Be specific, include studies, etc. - Studies conflict. It also appears to depends on the lights. Traditional LED lights have minor effect but seem to at least in part be a marketing ploy by companies promoting bleaching. Much of their whitening appears to come from temporary tooth drying during the light application. Violet LED lights have some promise as far as bleaching goes, but their bleaching effect appears to be independent of peroxide (meaning either the violet light or peroxides can bleach teeth similarly, but together they aren't synergistic or additive). However, these studies require long period of light exposure (i.e. 4 hours/day) (https://www.sciencedirect.com/science/article/abs/pii/S1572100020304063). However, this study wasn't in vivo. A systematic review showed a different result, that violet LED lights caused minor change, but not as much as peroxides, that could be additive. I would say the changes appear to minor and likely not worth the cost. (https://www.sciencedirect.com/science/article/abs/pii/S1572100022001028)
7. What are the benefits of peroxide vs. 'natural' or 'peroxide-free' options? What about PAP+? Does it work? Be specific, include studies, etc. - carbamide peroxide and hydrogen peroxide are the best studied compounds that have been shown to effectively whiten teeth. PAP has shown some promise but is not as proven as far as efficacy and safety. It is also much more expensive. (https://www.sciencedirect.com/science/article/abs/pii/S2452213919300191?via%3Dihub)
8. How much peroxide is safe to use in at-home products? And for how
long? What are the risks of overusing peroxide whitening
products? - normal, over-the-counter bleaching products are safe for nearly all people without existing tooth sensitivity or untreated dental disease. It can be used regularly without any significant long term side effects. Use does cause a reversible pulpitis (inflammation of the dental pulp), and so should not be used everyday, but time should be given to let the nerve settle before using it again. There are few risks, other than irritating untreated dental disease, especially teeth that need root canal therapy but have not been treated.
9. What are some preventive tips to keep your teeth white/maintain whitening results? - regular tooth brushing and visits to the dentist to get professional cleaning will remove any surface stains physically, but most bleaching/whitening is due to internal chemical bleaching. This discoloration occurs due to foods we eat, like coffee and curries. Compounds in these foods can get stuck between the crystal enamel rods in our teeth and cause discoloration. While you're welcome to change your diet around this, rather than changing your diet, it's more particular to just keep up with bleaching as needed.